JPH0540392A - Multicolor image formation device - Google Patents

Abstract

PURPOSE:To offer the multicolor image formation device which is free from image disordering and color mixture when development is repeated plural times on a photosensitive body where a toner image is already formed. CONSTITUTION:A developing unit which is applied with a developing bias voltage generated by superposing an AC component upon a DC component at the time of image area development is used as developing units of at least 2nd and succeeding toner image recording parts and the developing bias voltage of at least the DC component is applied continuously to the developing units of at least the 2nd and succeeding toner image recording parts from the start of 1st developing operation by one developing unit to the passage of a formed image at the final image recording part, so even if toner developed before a precedent stage is to leave the photosensitive unit and stick on the developing roll of the developing unit or mix when a developing unit in a trailing stage is put in operation, the toner is repelled by the DC component applied thereto and does not mix. Therefore, either the disordering of an image nor the color mixture is caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus for forming a multicolor image by one rotation of a photoconductor, and is particularly used for electrophotography, electrostatic recording, facsimile, transmission recording, laser printer and the like. And a multicolor image forming apparatus.

[0002]

2. Description of the Related Art There are various types of multicolor image forming apparatuses using electrophotography, one of which is to form a toner image on a photoconductor for each color and to form a toner image of each color. There is one in which a multicolor image is formed by sequentially superimposing and transferring on a recording paper. In this case, a charger, an exposure unit, a plurality of developing units corresponding to each color, a transfer unit, and a cleaning device are sequentially arranged around the drum-shaped photoconductor, and the charging and the exposure are performed for each rotation of the photoconductor. The process of developing, transferring, and cleaning is repeated. As a result, the toner images of the respective colors are sequentially superposed and transferred onto the recording paper for each rotation of the photoconductor to form a multicolor image.

Further, multi-color image formation by a one-time transfer method, in which toner images of respective colors are sequentially formed on a drum-shaped photoconductor for each rotation, and a multi-color image is formed on a recording paper by one-time transfer Devices are also known.

However, in the multi-color image forming apparatus of the one-transfer method and the one-transfer method, the photoconductor has to be rotated by the number of necessary colors, and thus until the final multi-color image is obtained. There is a problem that the time becomes longer.

In order to solve this problem, Japanese Patent Laid-Open No. 63-2
As disclosed in Japanese Patent No. 73883, a plurality of recording portions including a charging device, an exposure optical system and a developing device are arranged around a drum-shaped photoconductor, and a toner image of each color is formed during one rotation of the photoconductor. A multicolor image forming apparatus has been proposed in which a toner image of each color is formed on a photoconductor and is transferred onto a recording paper in one transfer process.

[0006] These multicolor image forming methods are desirable because they can be used in a wider range of use because they can also add color information as compared with information obtained by a black and white image.

By the way, the problems of these multicolor image forming systems are summarized as follows: (1) In the case of a system in which a toner image of each color is transferred every one rotation of the photoconductor, the transfer is performed every one rotation after the development of each color is completed. Since it is necessary to transfer the image on a sheet, the machine becomes large and the time required for image formation becomes long.

(2) In the one-time transfer method, the toner image forming operation is repeated and the toner images are sequentially overlapped, so that there is a color shift and a position shift of each toner image, and it is necessary to ensure accuracy. Further, the time required for image formation becomes long, as in the case of the transfer method for each rotation.

(3) In the case where a plurality of toner images are formed on the photoconductor and the transfer process is performed only once, if the photoconductor on which the toner image has already been formed is repeatedly developed a plurality of times, it is already formed in the subsequent development. The toner image formed on the photoconductor is disturbed, and the toner of the former stage adheres to and mixes with the developing roller of the latter stage, resulting in color mixing.

[0010]

By the way, one of the photoconductors is
When toner images of the respective colors are formed during rotation and the toner images of the respective colors are transferred in one transfer step, in order to avoid color mixture and mixture of toner, a toner image other than the developing device that first forms the toner image on the photoconductor is used. In the developing device, it has been proposed that the toner layer on the developing roll that conveys the developing toner and the photoconductor are not in contact with each other, and that a direct current component and an alternating current component are applied to the developing electric field applied to the developing roll during development. However, depending on the developing method, there is a problem that image distortion and color mixing do not disappear.

The present invention has been devised in order to solve the above-mentioned problems, and an object of the present invention is to distort an image or to cause color mixture when developing is repeated a plurality of times on a photoconductor on which a toner image is already formed. It is an object of the present invention to provide a multi-color image forming apparatus that does not have a color.

[0012]

In the multicolor image forming apparatus of the present invention, a plurality of image recording portions including a charging device, an exposing device and a developing device are sequentially arranged along the surface of a photoconductor, and the plurality of image recording devices are arranged. In a multi-color image forming method in which toner images of different colors are sequentially formed on the same portion or different portions of a photoconductor by a recording unit, a developing bias voltage applied to a developing roll of a developing device is controlled as follows during a developing operation. It was found that an accurate image of a predetermined color can be obtained without causing color mixing depending on how to select the developing bias voltage during non-operation.

That is, in the multicolor image forming apparatus of the present invention which achieves the above object, a plurality of toner image recording portions including a charging device, an exposing device and a developing device are sequentially arranged along the surface of a photoconductor, In a multi-color image forming apparatus that sequentially forms a plurality of toner images of different colors in one pass of the toner image recording unit at the same position or different positions of the photoconductor by at least the second and subsequent toner image recording units. A developing device for applying a developing bias voltage in which an alternating current component is superimposed on a direct current component at the time of image area development is used as the developing device for the image section,
A developing bias voltage applying means for continuously applying a developing bias voltage of at least a DC component from the start of the developing operation of any one of the developing devices until the formed image passes through the final image recording portion. It is characterized by.

In this case, the developing bias voltage applying means does not apply the developing bias voltage of the AC component to the developing device of at least the second and subsequent toner image recording portions while the developing device is not performing the developing operation. It is preferable to use a different material from the viewpoint of preventing the non-image area of the photoconductor from being soiled. Further, it is desirable that at least the second and subsequent toner image recording units are of a non-contact type in order to prevent image disturbance. In the following examples, a developing device using a magnetic two-component developer is used.

[0015]

According to the present invention, at least the second and subsequent toner image recording units are used as a developing device for applying a developing bias voltage in which an AC component is superimposed on a DC component at the time of image area development. A developing bias voltage of at least a DC component is continuously applied to the developing unit of the image recording unit from the start of the developing operation of one of the developing units until the image formed on the final image recording unit passes. Since the developing bias voltage applying means is provided, when the developing device in the subsequent stage is not operated, that is, when the development of the color is not performed, and when the non-image area of the photoreceptor reaches the developing device, Even if the previously developed toner leaves the photoconductor and tries to adhere to and mix with the developing roll of the developing device, it is repelled by the DC component applied to it and adheres and mixes. Can not. Therefore, image distortion and color mixing do not occur.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be specifically described below with reference to the drawings based on the embodiments. FIG. 1 is a side view showing an embodiment of a multicolor image forming apparatus of the present invention. The multi-color image forming apparatus 50 includes an image forming section 1 above the apparatus and a sheet feeding section 2 below. In the image forming unit 1, the translucent belt-shaped photosensitive member 3 is vertically arranged around the driving roller 4a, the idler rollers 4b to 4e, and the like. The belt-shaped photoconductor 3 is moved by the drive roller 4a so that the arrow A
Driven to rotate. Around the belt-shaped photoreceptor 3, the first image recording unit 5, the second image recording unit 6, the third image recording unit 7, the fourth image recording unit 8, the pre-transfer corotron 9, the developing density sensor 10b, A light guide unit 11, a transfer unit 12, a pre-cleaning corotron 13, a cleaning device 14, and a ground strip 15 are arranged. The components forming each of these image recording units and the like are arranged along a substantially vertical surface of the belt-shaped photoconductor 3. Further, inside the lower end portion of the belt-shaped photosensitive member 3, there are disposed static elimination lamps 16 that irradiate the belt-shaped photosensitive member 3 from the inside before and after the transfer section 12.

The transfer section 12 is a transfer corotron 12a.
Also, the peeling corotron 12b is provided, and is arranged at the lowermost end of the vertically long belt-shaped photoconductor 3 so that the paper conveyance direction is substantially horizontal. Further, adjacent to the transfer unit 12, a sheet conveying device 17 and a conveying roller 18 are provided on the sheet introducing side, and a conveying belt 20 for conveying the recording sheet after transfer to the fixing device 19 is provided on the sheet discharging side. ..

The first image recording section 5 includes the first charger 2
1. Laser light source (not shown), rotary polygon mirror 22a irradiated with laser light, motor 22b for rotationally driving this rotary polygon mirror 22a, lenses 22c and 22d, mirrors 22e and 22.
A first exposure device 22, a first potential sensor 23, a first developing device 24, and the like, which are configured by f and the like, are provided. In addition, the second image recording unit 6 includes a second charger 25, a second exposure device 26 including a light emitting diode array (LED array), a second potential sensor 27, a second developing device 28, and the like. Similarly, the third and fourth image recording units 7 and 8 are also provided with the third and fourth chargers 2.
9, 33, 3rd, 4th exposure apparatus 30, 34, 3rd, 4th
Potential sensors 31, 35, third and fourth developing devices 32, 36, etc. are provided.

The first, second, third, and fourth image recording units 5, 6, 7, and 8 are, for example, black, red, and
An image of each color is formed on the belt-shaped photoconductor 3 by using toners of each color of green and blue. In addition, each potential sensor 23,
Reference numerals 27, 31, 35 detect the surface potential of the belt-shaped photoconductor 3 in each of the image recording units 5, 6, 7, 8 and set a predetermined potential (described later) so that a control circuit (not shown) is provided. )
The respective chargers 21, 25, 29, 33 are controlled by. Further, the final development density is detected by the development density sensor 10b, and the development conditions in each of the image recording units 5, 6, 7, and 8 are adjusted so that an appropriate density is obtained. In addition,
The developing density sensor 10b is configured by arranging color sensor elements corresponding to each color in a direction perpendicular to the moving direction of the photoconductor 3. The developing units 24, 28, 32, 36 are
The developing rolls 24a, 28a, 32a, 36a and the backup rolls 24b, 28b, 32b, 36b are provided, respectively. Second, third, and fourth developing units 28, 32, 3
No. 6 does not cause the toner image formed on the photoconductor 3 by the preceding developing device to be disturbed, so a non-contact type developing device is adopted. The details will be described later.

The paper feeding unit 2 includes an intermediate tray 41 having paper feeding devices 37, 38, 39 and 40, paper feeding trays 42 and 43, a large capacity tray 44, and a paper reversing unit 4.
5 etc. are arranged. The intermediate tray 41 is provided with a switching claw device 46 having a plurality of switching claws 46a, 46b, 46c. Incidentally, 47 and 48 are conveying rolls, and 49 is a reversing roll.

Next, a circuit configuration for forming an image in the above-described multicolor image forming apparatus 50 will be described with reference to FIG. Image signals from the image input device 51, the computer 52, the communication device 54 that performs communication via the communication line 53, and the like are supplied to the multicolor image forming device 50 through the image processing device 55. The image signal supplied to the image processing device 55 is first to
The fourth color component signal is separated into, for example, four color component signals of black, red, green, and blue, and the first color component signal is substantially not delayed and the first exposure device 22 of the first recording unit 5 is separated. And the second to fourth color component signals are supplied to the second to fourth recording units 6 to 8 via the first to third delay circuits 57 to 59, respectively.
~ It is supplied to the fourth exposure device 26, 30, 34. In addition,
Delay time T ₁ in the first to third delay circuits 57 to 59,
T ₂ and T ₃ correspond to the distances of the exposure positions of the belt-shaped photoconductor 3 by the second to fourth exposure devices 26, 30, and 34 from the exposure position of the first exposure device 22. However, each of the delay circuits 57 to 59 is a variable delay circuit,
The delay time can be slightly changed based on an instruction from the microcomputer 60. As the delay circuit, for example, a delay circuit using a BBD (bucket relay type charge transfer device) can be adopted, and the delay is performed by changing the frequency of the transfer clock for the BBD according to the control data from the microcomputer 60. The time can be changed continuously. Further, switching circuits 61 to 64 controlled by the microcomputer 60 are provided in the paths of the respective color component signals, and these switching circuits 61 to 64 are connected to the pattern generation circuit 65 controlled by the microcomputer 60. Test pattern signal is supplied.

The first to fourth chargers 21, 25, 29, 33 of the recording units 5 to 8 and the first to fourth exposure devices 22 and 2 are also provided.
6, 30, 34, first to fourth developing devices 24, 28, 32,
The operation of 36 is controlled by the control device 66 that operates based on an instruction from the microcomputer 60. Further, an operation panel 67 for inputting various instructions to the copying machine and a non-volatile memory 68 for storing control data for the delay circuits 57 to 59 are connected to the microcomputer 60.

First, regarding the image forming mode, red and black 2
A case of forming a color image will be described as an example. In this case, when the operation panel 67 is instructed to operate the apparatus in the image forming mode and further an image is formed in two colors of red and black, the microcomputer 60 causes the switching circuits 61 to 64 to perform color separation. While being switched to the circuit 56 side, the control device 66 enables only the first and second image recording units 5 and 6, and disables the third and fourth image recording units 7 and 8. This operation / non-operation switching is performed by, for example, the first and second chargers 21, 2
5, by applying a predetermined operating voltage or bias voltage only to the first and second exposure devices 22 and 26. However, as will be described later, the third and fourth developing devices 32,
A direct-current developing bias voltage is continuously applied to 36.

The belt-shaped photosensitive member 3, which is rotationally driven in the direction of arrow A by the driving roller 4a, first has the first image recording unit 5
In FIG. 3, the first charger 21 uniformly charges the toner as shown in FIG. As a result, the surface potential of the photoconductor 3 becomes, for example, V _P (where V _P is a negative value). Next, in the first exposure device 22, the surface of the photoconductor 3 is exposed by the light L _k from the laser modulated by the signal corresponding to the black of the image, and the potential of the exposed portion is, for example, V _R (however,
V _R decreases to a negative value (see (b) in the figure). Next, this exposed portion advances to the first developing portion 24, where it is developed with the black toner T _k (see FIG. 7C). Even after this development, the surface potential of the black image portion remains lowered.

Next, the black developing portion advances to the second image recording portion 6, is charged again by the second charger 25, and the photoconductor 3
Surface potential rises to near V _P (see FIG. 7D). Next, in the second exposure device 26, the surface of the photoconductor 3 is exposed by the light L _R from the light emitting diode array modulated by the signal corresponding to the red color of the image, and the potential of the exposed portion drops to V _R. .. (Refer to the same figure (e)). Next, this exposed portion advances to the second developing portion 28 where it is developed with the red toner T _R (see FIG. 7F). After this red development, the surface potential of the red image portion remains low.

The belt-shaped photosensitive member 3 further advances and passes through the third and fourth image recording portions 7 and 8, but since these image recording portions 7 and 8 are inoperative, toner images of respective colors are not formed. Not affected.

Next, the toner image is adjusted in electric charge by the pre-transfer corotron 9 and the charge eliminating lamp 16 to be in a state suitable for transfer.

When the toner images of the respective colors reach the transfer unit 12, in synchronization therewith, the recording paper is conveyed from any one of the trays 41 to 44 of the paper feeding unit 2 by any one of the paper feeding devices 37 to 40. The sheet is fed to the image forming unit 1 side along B, is further conveyed by the sheet conveying device 17 and the conveying roller 18, and comes into contact with the surface of the belt-shaped photoreceptor 3.

In the transfer section 12, the toner image of each color is transferred from the surface of the belt-shaped photoconductor 3 to the recording paper by the electric field from the transfer corotron 12a. The recording paper after the transfer is separated from the belt-shaped photoconductor 3 by the separating corotron 12b and is conveyed to the fixing device 19 by the conveying belt 20 to fix the toner image on the recording paper. The recording paper after fixing advances in the direction of arrow C, for example, and is directly discharged out of the apparatus by the conveying roller 47 with the image surface facing upward. When the image surface is to be ejected downward, the sheet is once conveyed by the conveying rollers 48 and 49 in the directions of arrows D and E, and then the conveying rollers 48 and 49.
The rotation of 9 is reversed, and it is carried out of the machine by the carrying roller 47.

The toner remaining on the photosensitive member 3 on the belt after the transfer is removed by the cleaning device 14 after the charge state is adjusted by the charge eliminating lamp 16 and the bri-cleaning corotron 13. Further, the electric charge remaining on the photoconductor 3 is discharged through the ground strip 15 to prepare for the next image forming cycle.

In the case of double-sided copying, the recording paper after fixing advances in the direction of arrow D, is fed to the paper reversing unit 45 of the paper feeding unit 2 by the conveying roller 48, and is temporarily moved in the direction of arrow E by the reversing roller 49. After being conveyed, the rotation of the reversing roller 49 is reversed, the conveying direction of the recording paper is reversed in the arrow F direction, and the recording paper is stored in the intermediate tray 41 with the image surface facing upward. At this time, by changing the postures of the switching claws 46a, 46b, 46c of the switching claw device 46 according to the size of the recording paper,
The recording paper is stored in the intermediate tray 41 from an appropriate position. This recording paper is sent to the transfer unit 12 of the image forming unit 1 again by the paper feeding device 37, and the image on the back surface of the recording paper is formed this time. In the case of double-sided printing, it goes without saying that a toner image is formed by the image forming unit 1 on each side.

The above is a description of the case of forming a two-color image of red and black, but the image forming operation is clear from the above description even when the image recording units 7 and 8 are also operated to form an image in multiple colors. Will.

The main operation parameters of the multicolor image forming apparatus 50 of the above embodiment will be described below.
The belt-shaped photoconductor 3 has a weekly speed of 200 mm / sec and an arrow A.
Driven to rotate. The belt-shaped photoconductor 3 has its surface uniformly charged to −580 V by the first charger 21 in the first image recording section (see FIG. 3A). Next, the surface of the photoconductor 3 is irradiated with laser light in the first exposure device 22 based on the black color signal, and about −100 V is applied.
Latent image is formed (see FIG. 3B). Then, it is subjected to reversal development by the black developing device 24, and a black toner image is formed on the surface of the photoconductor 3 (see (c)). The black developing device 24 is a conventionally used two-component type of contact type (type in which the ears of development are in contact with the surface of the photoconductor), and the developing potential is −.
430V was applied.

In the second image recording section 6, the second charger 2
5, the history of the previous image is erased, and the black developing toner portion is recharged so that the black developing toner portion becomes −490 V and the background potential becomes −600 V so that the image formation in the next step can be performed (FIG. 3).
(See (d)). Subsequently, based on the red color signal, a latent image is formed at about −100 V by the LED array of the second exposure device 26 (see FIG. 3E), and the non-contact red developing device 28 performs reverse development. , A red toner image was formed (Fig. 3
(See (f)).

As described above, the second to fourth developing devices 28, 32, and 36 should not disturb the toner image formed on the photoconductor 3 by the preceding developing device, and therefore, are not in contact with each other. A mold developing device is adopted. These developing devices 2
8, 32, and 36 have the same structure, the structure of the second developing device 28 will be described as an example in FIG. The developing roll 28a, the mag roll 28d, the trimmer 28f, and the auger 28e are sequentially arranged. In the rear part of the developer housing 28c, a magnetic two-component developer is circulated by the auger 28e, and a part of this developer is supplied from the DC power supply 28g, for example, -200 to -60.
Only the toner in the developer is attached to the mag roll 28d biased to 0V and further from the mag roll 28d to the developing roll 28a. The developing roll 28a has 1000 to 10000 Hz, 500 to 1 Hz from the AC power source 28h.
-200 from the DC power supply 28i for the AC component of 500V
A bias voltage in which a DC component of -600 V is superimposed is applied. The developing roll 28a has a surface layer of 10 ¹⁰
It has a resistance layer of Ωcm or more, and the distance between the surface of the developing roll 28a and the surface of the belt-shaped photoreceptor 3 is 200 to 500 μm.
It is set to m.

The voltage applied to the red developing device 28 is the mag roll 2
8d DC voltage of -550V and developing roll 28a
Includes a rectangular wave of 5000 Hz with an AC voltage of 1.5 kV,
DC voltage of -490V is applied. The developing roller 28a has a diameter of 25 mm and is rotated at 300 rpm, and the gap between the developing roller 28a and the photoconductor 3 in the developing area is 300 μm.
It is set to m.

In the third image recording section 7, the third charger 2
9, the red developing toner portion was recharged to −520V and the background potential was −620V. Then, based on the green color signal, the third exposure device 30
A latent image is formed at about -100 V by the LED array of the above, and is formed on the developing roll of the non-contact developing device 32 similar to the red developing device 28.
AC component of 1.5 kV and 5000 Hz, and DC component-
520 V was applied, and reversal development was performed in the same manner as above, and a green toner image was formed.

In the fourth image recording section 8, recharging was carried out by the fourth charger 33 so that the green developing toner section was -540V and the background potential was -640V. Then, based on the blue color signal, the fourth exposure device 3
A latent image is formed at about -100V by the 4 LED array,
Reverse development was carried out on a developing roll of the non-contact developing device 36 similar to the red and green developing devices with a DC component of -540 V and the other components were similarly developed to form a blue toner image.

An image is formed under the above conditions, and the photoconductor 3
The color mixing ratio of the developer caused when the toner image formed above is mixed in the developing device in the subsequent stage was evaluated as follows. That is, the black toner image formed on the photoconductor 3 by the first image recording unit 5 reaches the second red developing device 28, and is separated from the photoconductor 3 and flies onto the developing roll 28a, and the red developing device 28 The amount mixed in the developing roll 28a is in a state in which the potential of the developing roll 28a is grounded, the state in which no voltage is applied to the developing roll 28a but it is floated from ground,
a in which a DC bias voltage of -490 V is applied to a
For each of the two cases, after making 100 copies, the development was stopped and the relative mixing ratio was evaluated, as shown in FIG.

What is apparent from this result is that when the developing device in the subsequent stage is not operated, that is, when the development of the color is not performed, and when the image area of the photoconductor reaches the developing device, When alternating current or direct current applied to the developing roll of the developing device is cut to float electrically or ground, the toner developed before the preceding stage separates from the photoconductor 3 and adheres to and mixes with the developing roll to form a formed image. Color mixing will occur. On the other hand, it can be seen that such a phenomenon hardly occurs if the DC component is continuously applied.

Therefore, in the present invention, in order to prevent the toner image on the photoconductor 3 from flying to the developing roll of the developing device of the next stage and thereafter, at least one of the developing devices of the preceding stage and above operates to form a toner image. , Until the image area passes
Regardless of whether the developing device in the subsequent stage operates or does not develop, the DC component is always applied to the developing device.

For example, when the image forming operation is performed in all the image recording units 5 to 8, as shown in the operation timing chart of each unit in FIG. 6, the second, third and fourth developing units 28 and 3 are provided.
By applying a DC component from the start of the first black developing device operation to the OFF state of the AC component of the fourth developing device 36, developers 2 and 36 are mixed with toner of other colors. Is no longer mixed.

Further, for example, when only the black image recording unit 5 and the red image recording unit 6 are operated, as shown in FIG. 7, the AC component of the second developing device 28 is turned off and the final image recording unit is turned off. Until the image passes through the third and fourth developing devices 3
The DC component is continuously applied to the developing rolls 2 and 36 so that the black and red toners are not mixed in the green developing device 32 and the blue developing device 36.

The control device 66 controls the application of the developing bias voltage of the developing devices 28, 32, 36 at the above timing based on the control signal from the microcomputer 60.

The multicolor image forming apparatus of the present invention has been described above based on the embodiments, but the present invention is not limited to these embodiments and various modifications can be made. For example,
It can also be applied to the one using a one-component developing device.

[0046]

As described above, according to the multicolor image forming apparatus of the present invention, as a developing device of at least the second toner image recording portion, a developing bias in which an AC component is superimposed on a DC component at the time of image area development is developed. By applying a voltage, the developing device of at least the second toner image recording unit and the developing device of any one of the developing units first start the developing operation, and then the image formed on the final image recording unit passes through. Until
Since the developing bias voltage applying means for continuously applying the developing bias voltage of at least the DC component is provided, when the developing device in the subsequent stage is not operated, that is, when the development of the color is not performed, and the image area of the photoconductor is When it reaches the developing unit, the toner developed before the previous stage separates from the photoconductor and tries to adhere to or mix with the developing roll of the developing unit, but it is repelled by the DC component applied to it and adheres or mixes. I can't. Therefore, image distortion and color mixing do not occur.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of a multicolor image forming apparatus of the present invention.

2 is a diagram showing a circuit configuration for forming an image of the apparatus of FIG.

FIG. 3 is a diagram showing the relationship between each process and the surface potential in the apparatus of FIG.

FIG. 4 is a cross-sectional view showing a configuration example of a developing device.

FIG. 5 is a diagram showing a result of measuring an amount of toner mixed in a developing device in relation to a developing roll potential state.

FIG. 6 is a diagram showing an example of an operation timing chart of each unit according to the present invention.

FIG. 7 is a diagram showing another example of an operation timing chart.

[Explanation of symbols]

1 ... Image forming unit, 2 ... Paper feeding unit, 3 ... Belt-shaped photoconductor, 4
a ... drive roller, 4b-4e idler roller, 5 ... first
Image recording unit, 6 ... Second image recording unit, 7 ... Third image recording unit, 8 ... Fourth image recording unit, 9 ... Pre-transfer corotron, 10b ... Development density sensor, 11 ... Light guiding unit, 1
2 ... Transfer part, 12a ... Transfer corotron, 12b ... Peeling corotron, 13 ... Pre-cleaning corotron, 14 ...
Cleaning device, 15 ... Ground strip, 16 ... Static elimination lamp, 17 ... Paper transport device, 18 ... Transport roller, 19
... fixing device, 20 ... transport belt, 21 ... first charger, 2
2 ... First exposure device, 22a ... Rotating polygon mirror, 22b ... Motor, 22c, 22d ... Lens, 22e, 22f ... Mirror, 2
3 ... 1st electric potential sensor, 24 ... 1st developing device, 25 ... 2nd charging device, 26 ... 2nd exposure apparatus, 27 ... 2nd electric potential sensor, 2
8 ... 2nd developing device, 29 ... 3rd charging device, 30 ... 3rd exposure device, 31 ... 3rd electric potential sensor, 32 ... 3rd developing device, 33 ...
Fourth charger, 34 ... Fourth exposure device, 35 ... Fourth potential sensor, 36 ... Fourth developing device, 24a, 28a, 32a, 36
a ... developing roll, 24b, 28b, 32b, 36b ... backup roll, 37, 38, 39, 40 ... sheet feeding device, 41 ... intermediate tray, 42, 43 ... sheet feeding tray, 44
... large-capacity tray, 45 ... paper reversing section, 46 ... switching claw device, 46a, 46b, 46c ... switching claw, 47, 48 ... transport roll, 49 ... reversing roll, 50 ... multicolor image forming device, 51 ... image input Device, 52 ... Computer, 53 ...
Communication line 54 ... Communication device 55 ... Image processing device 56
... Color separation circuit, 57 to 59 ... First to third delay circuits, 60
... Microcomputer, 61-64 ... Switching circuit, 65
... pattern generating circuit, 66 ... control device, 67 ... operation panel, 68 ... non-volatile memory, 28c ... developer housing, 28d ... mag roll, 28f ... trimmer, 28e ... auger, 28g ... DC power supply, 28h ... AC power supply, 28i …
DC power supply

Claims (4)

[Claims] 1. A plurality of toner image recording portions including a charging device, an exposing device and a developing device are sequentially arranged along the surface of a photoconductor, and a plurality of toner images of different colors are formed by one pass of the photoconductor. In a multicolor image forming apparatus that sequentially forms a plurality of toner image recording units at the same or different positions of a photoconductor, as a developing device for at least the second and subsequent toner image recording units, a DC component and an AC component are used during image area development. Is applied to the developing devices of at least the second and subsequent toner image recording units, and any one of the developing devices is the last until the image formed on the final image recording unit passes. A multicolor image forming apparatus comprising: a developing bias voltage applying unit that continuously applies a developing bias voltage of at least a DC component until the developing operation is completed. 2. The developing bias voltage applying means does not apply an AC component developing bias voltage to at least the second and subsequent developing devices of the toner image recording portion while the developing device is not performing a developing operation. The multicolor image forming apparatus according to claim 1, wherein the multicolor image forming apparatus is provided. 3. The multicolor image forming apparatus according to claim 1, wherein at least the second and subsequent toner image recording units are non-contact type developing devices. 4. The multicolor image forming apparatus according to claim 1, wherein each of the developing devices uses a magnetic two-component developer.